On average, listings lease in the $20's per square foot per year. The O'Fallon region is going through a a rise in rates. In the last 3 months, the median rate went up $22 per sqft per year.
In the last 90 days, 31 listings have come on the market, which means new listings are probably going fast. You'll want to be prepared to make an offer immediately. About 19% of the available leases in the O'Fallon are subleases, so you might be able to snag a great spot on a short term. There aren't many listings below 2,000 square feet on the market, so finding a space for a small business might be tough.
Even though the median size is 22,780 sqft, there are still 0 leases below 2,000 sqft. Most properties in this market are approximately 2 floors. Most buildings in this market were built in 2001 and are Class A.